The invention relates to a tensioning device for tensile stressing (extending) a threaded bolt on its thread end portion, having a cylindrical housing which is supported against a fixed abutting base and has at least one piston, moveable in a longitudinal direction therein and connectable to a hydraulic supply, and having an interchangeable sleeve, which leads centrally through the piston, at its end having an internal thread with an engagement length that can be screwed onto the thread end portion, the sleeve being provided with a radially expanded portion designed to be carried axially by a carrier face formed on the piston.
U.S. Pat. No. 8,375,554 B2 discloses a hydraulically functioning bolt tensioning device having these features. For stressing the threaded bolt an interchangeable sleeve, which is provided at its lower end with an internal thread for screwing to the threaded bolt, is arranged in the cylindrical housing of the tensioning device. The interchangeable sleeve can be carried axially by a hydraulically actuated piston of the tensioning device, and for this purpose is provided with a radially expanded flange or collar.
Bolt tensioning devices having multiple interchangeable sleeves are also disclosed by U.S. Pat. No. 8,616,094 B2, for example. Here the inner interchangeable sleeve is displaceable in an axial direction relative to the outer interchangeable sleeve and is pre-sprung against the outer interchangeable sleeve. After screwing on the interchangeable sleeves the bolt is axially tensioned by two hydraulically operated pistons, which move the outer and the inner interchangeable sleeves simultaneously in an axial direction. The total pre-tensioning force is transmitted to two separate threads of the bolt by a thread of the inner interchangeable sleeve and thread of the outer interchangeable sleeve.
In the case of a bolt tensioning device disclosed by US 2011/0271798 A1 also, the threaded bolt is axially stressed by means of an interchangeable sleeve engaging in the thread of the threaded bolt. This sleeve can be carried axially by pistons of the tensioning device arranged in series, in that the interchangeable sleeve is provided close to its upper end with a thread, onto which a flange or collar, undercut by the uppermost piston, is screwed. A spring arrangement arranged around the interchangeable sleeve is supported against the collar and in addition against the interchangeable sleeve so that the latter always bears against the uppermost piston. In order to screw the interchangeable sleeve onto the threaded bolt, the tensioning device is mounted onto the threaded bolt from above and rotated about its axis so that the interchangeable sleeve is screwed onto the free threaded portion of the threaded bolt.
Screwing the tensioning device on in this way and rotating it about its axis is time-consuming and in view of the weight of such bolt tensioning devices also laborious. Moreover, mounting the heavy tensioning device leads to a sometimes hard, uncontrolled collision between the threaded portion of the interchangeable sleeve and the threaded bolt, which may cause damage to the threads involved.
It is the object of the invention, through design measures on the tensioning device, to avoid the interchangeable sleeve coming into premature contact with the threaded bolt whilst mounting the bolt tensioning cylinder, and in this way to prevent damage to the threads involved.